The present invention relates generally to Micro-Electro-Mechanical Systems (MEMS) devices, and more particularly to a method for fabricating high-aspect-ratio device with integrated circuit on the same substrate using post-CMOS microfabrication techniques.
Micro-electro-mechanical systems (MEMS) technology has received increasing attention in recent years. Compared with conventional devices, MEMS devices have advantages in size, weight, cost and power consumption, so they are very attractive for space navigation, military, medicine and automobile application. However, the performance of present MEMS sensors, such as MEMS gyroscopes, especially the accuracy, is not as good as that of conventional sensors.
Recently, a great deal of interests have developed in manufacture processes that allow the monolithic integration of MEMS structures with driving, controlling, and signal processing electronics. This integration promises to improve the microsystem performance of micromechanical devices and potentially lower the cost of device manufacturing and packaging. A modular integration approach is attractive because it allows for separate development of micromechanics and microelectronics technology components. Many processes have been proposed to allow integration MEMS and ICs, such as post-CMOS, pre-CMOS, and hybrid-CMOS processes. In these processes, the post-CMOS process is the more conducive to the use of integrated circuit (IC) foundries for low-cost electronics fabrication. For example, the circuits can be fabricated in any IC foundries using standard cells and their standard IC technology firstly without any MEMS or other process steps. The MEMS could then be fabricated on the IC Wafers.
U.S. Pat. No. 6,121,552 discloses a microfabricated high aspect ratio device, and the formation of the device comprises three steps subsequently: forming an isolation trench, forming circuit region and electrical interconnection, and formation of structure region. Therefore, a pre-CMOS technique is employed in the U.S. Pat. No. 6,121,552.
However, in most cases, the post-CMOS processes are surface micromachining, whose microstructures height is limited to the thickness of the deposited thin film. Moreover, release holes and unwanted curvature of microstructures degrade their application. Furthermore, the post-CMOS necessitates a low thermal budget for the MEMS structure fabrication process, if circuits employing conventional aluminum or copper metal interconnections are used.
A CMOS-MEMS lateral-axis bulk micromachined gyroscope has been reported by Carnegie Mellon University. However, this approach suffers the residual stress and the thermal expansion coefficient in the thin metal/dielectric layers cause curling.
Another problem of prior arts is the formation of void during the refilling of trenches. U.S. Pat. No. 6,291,875 discloses a method for removing the void, in which various condyles are formed and then inserted into the voids. Obviously, this method significantly increases the complexity and cost of forming the device.
Accordingly, there is a need for a method to fabricate high-aspect-ratio silicon MEMS structure with CMOS circuits in same substrate using post-CMOS process, which can increase the accuracy and reliability of MEMS sensors as well as lower the fabricating cost.